LSM Mirrorred Volumes ( Distance Limit ) ?

[Srivathsan_2]

I remember reading the LSM documentation that LSM mirrored plexes are synchronous in terms of data updates.

I am trying to explore the possibility of having an ES40 and HSG80 in one site ( fiber connection of 10 meters ) and another HSG80 available in a remote site ( 9.5 Kms away ).

The LUNs provided by these 2 HSG80s are to be mirrored using LSM.

The remote site would have a cold-standby ES40 available to import the local HSG80 diskgroup and start catering to users asap.

Wondering if there is any limitation imposed by distance between the physical disks ( forming the subdisks associated with each mirrored plex ) ?

Also welcome are any comments or suggestions on this design !!

[Srivathsan_2]

Okay, forgot to add :-)

The cold-standby ES40 would kick-in and import it's local HSG80 diskgroup only in the event of a disaster at the main site.

Thanks

[Florian Heigl (new acc)]

there are limitations from signal run times and SAN switch types, but (I dare say) from LSM itself.

And I think 9KM is below the limit were one needs to use DWDM links or needs special brocade licenses, so You shold be fine.

One thing I'd like to add is that 'synchronous' is not 100% correct, but almost. (the dirty region log will enforce mirror consistency, but You still might have to rollback You databases a minute)

Of course this is still a great and usually completely acceptable thing in a disaster situation when compared to ordering tape drives and recovering at the D/R site :)

[Ivan Ferreira]

The distance will be ruled by the specifications of the storage device (SAN distance limits), but you should be worried about the availability of the link and remote site, and the I/O of the filesystems.

We tryied to use LSM as an disaster recovery solution, but our test showed very poor performance, unaceptable. So now we are using Continuous Access.

And the recovery of a stale/failed LSM mirror can be tedious.

[Mulgund]

If LSM doesn't look good, StorageWorks Data Replication Manager can be one solution for this requirement.
Chk. http://cybrary.inet.cpqcorp.net/SW/LP/SYSMGT/STORAGE/DRM/index.html?/SW/LP/SYSMGT/STORAGE/DRM/resources.html for details.

-Srinivas